CHAPTER XVIII. 



CLASSIFICATION AND ADDITIONAL STUDIES OF 

 THE ALG^E. 



In order to show the general relationship of the algae studied, the princi- 

 pal classes are here enumerated as well as some of the families. In some 

 of the groups not represented by the examples studied above, a few species 

 are described which may serve as the basis of additional studies if desired. 

 The principal classes * of algae are as follows: 



Class Chlorophyceae. 



331. These are the green algae, so called because the chlorophyll green 

 is usually not masked by other pigments, though in some forms it is. There 

 are three subclasses. 



332. Subclass PKOTOCOCCOIDE.^. In the Protococcoideae are found the 

 simplest green plants. Many of them consist of single cells which live an 

 independent life. Others form "colonies," loose aggregations of individ- 

 uals not yet having attained the permanency of even a simple plant body, 

 for the ce\ls often separate readily and are able to form new colonies. The 

 colonies are often held together by a gelatinous membrane, or matrix. 

 Some are motile, while others are non-motile. A few of the families are 

 here enumerated. 



333. Family Volvocaceae. These are all motile, during the vegetative 

 stage. The individuals are single or form more or less globose colonies. 



334. The "red snow" plant (Sphaerella nivalis). This is often found in 

 arctic and alpine regions forming a red covering over more or less large 

 areas of snow or ice. For this reason it is called the "red snow plant." 



335. Sphaere'.la lacustris, a closely related species, is very widely dis- 

 tributed in temperate regions along streams or on the borders of lakes and 



* In Engler & Prantl's Pflanzenfamilien, Wille uses the term class for 

 these principal subdivisions of the algae. Syshmatists are not yet agreed 

 upon a uniform use of the term?. 



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